Direct application voltage variable material, devices employing same and methods of manufacturing such devices

ABSTRACT

A voltage variable material (“VVM”) including an insulative binder that is formulated to intrinsically adhere to conductive and non-conductive surfaces is provided. The binder and thus the VVM is self-curable and applicable in a spreadable form that dries before use. The binder eliminates the need to place the VVM in a separate device or to provide separate printed circuit board pads on which to electrically connect the VVM. The binder and thus the VVM can be directly applied to many different types of substrates, such as a rigid FR-4 laminate, a polyimide, a polymer or a multilayer PCB via a process such as screen or stencil printing. In one embodiment, the VVM includes two types of conductive particles, one with a core and one without a core. The VVM can also have core-shell type semiconductive particles.

PRIORITY CLAIM

This application claims the benefit as a continuation-in-part of U.S.patent application Ser. No. 10/746,020, filed Dec. 23, 2003, entitled“Direct Application Voltage Variable Material, Components Thereof AndDevices Employing Same,” which claims the benefit as acontinuation-in-part of U.S. patent application Ser. No. 10/410,393,filed Apr. 8, 2003, entitled “Voltage Variable Material For DirectApplication And Devices Employing Same,” which claims the benefit ofU.S. Provisional Patent Application No. 60/370,975, filed Apr. 8, 2002,entitled “Voltage Variable Material For Direct Application And DevicesEmploying Same,” the entire contents of each which are herebyincorporated by reference and relied upon.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to the following commonly-owned co-pendingpatent applications: “Voltage Variable Substrate Material,” Ser. No.09/976,964, Attorney Docket No. 0112690-098.

BACKGROUND OF THE INVENTION

The present invention generally relates to circuit protection. Morespecifically, the present invention relates to voltage variablematerials.

Electrical overstress (“EOS”) transients produce high electric fieldsand usually high peak power that can render circuits or the highlysensitive electrical components in the circuits, temporarily orpermanently non-functional. EOS transients can include transientvoltages capable of interrupting circuit operation or destroying thecircuit outright. EOS transients may arise, for example, from anelectromagnetic pulse, an electrostatic discharge, lightning, a build-upof static electricity or be induced by the operation of other electronicor electrical components. An EOS transient can rise to its maximumamplitude in subnanosecond to microsecond times and have repeatingamplitude peaks.

Materials exist for the protection against EOS transients, which aredesigned to respond very rapidly (ideally before the transient wavereaches its peak) to reduce the transmitted voltage to a much lowervalue for the duration of the EOS transient. EOS materials arecharacterized by high electrical resistance values at low or normaloperating voltages. In response to an EOS transient, the materialsswitch very rapidly to a low electrical resistance state. When the EOStransient dissipates, these materials return to their high resistancestate. EOS materials also recover very rapidly to their original highresistance value upon dissipation of the EOS transient.

EOS materials are capable of repeated switching between the high and lowresistance states. EOS materials can withstand thousands of ESD eventsand recover to desired off-status after providing protection from eachof the individual ESD events.

Circuits employing EOS materials can shunt a portion of the excessivevoltage or current due to the EOS transient to ground, protecting theelectrical circuit and its components. Another portion of the threattransient reflects back towards the source of the threat. The reflectedwave is attenuated by the source, radiated away, or re-directed back tothe surge protection device, which responds in kind to each return pulseuntil the threat energy is reduced to safe levels. A typical circuitemploying an EOS transient device is illustrated in FIG. 1.

With reference to FIG. 1, a typical electrical circuit 10 isillustrated. The circuit load 12 in the circuit 10 operates at a normaloperating voltage. An EOS transient of substantially more than two tothree times the normal operating voltage having a sufficient durationcan damage the load 12 and the components contained therein. Typically,EOS threats can exceed the normal operating voltage by tens, hundreds oreven thousands of times the voltages seen in normal operation.

In the circuit 10, an EOS transient voltage 14 is shown entering thecircuit 10 along line 16. Upon the occurrence of the EOS transientvoltage 14, an EOS protection device 18 switches from the highresistance state to a low resistance state thus clamping the EOStransient voltage 14 at a safe, low value. The EOS protection device 18shunts a portion of the transient threat from the electronic line 16 tothe system ground 20. As stated above, the EOS protection device 18reflects a large portion of the threat back towards the source of thethreat.

EOS protection devices typically employ a voltage variable material(“VVM”). VVM's have typically been of a consistency and make-uprequiring some form of housing or encapsulation. That is, the VVMmaterials have heretofore been provided in a device, such as a surfacemount device, mounted to a printed circuit board (“PCB”). The VVMdevices have typically been mounted discretely from the devices of thecircuit that require protection. This presents a variety of problems.

First, VVM devices add to the number of components that are required tobe mounted to the PCB. The VVM devices consume valuable board space andadd to the potential for defects. The VVM devices typically require thatadditional pads be secured to the PCB and that additional circuit tracesbe routed from the PCB devices or from a ground plane to the VVM pads.It is always desirable for cost, spacing/flexibility and reliabilitypurposes, to reduce the number of components mounted to a PCB.

Second, adding components to an existing PCB can require a boardredesign or other type of incorporation into a currently pending design.If the application is already in production, it is likely that aconsiderable amount of time has been spent optimizing board space, whichmay or may not leave room to integrate a VVM device.

Third, many EOS transients occur outside of the PCB and are transmittedto the PCB through cables and wires. For instance, networked computerand telephone systems are subject to a variety of transients caused byenvironmental and handling activities. In these situations, it would bedesirable to eliminate voltage transients before they reach the PCB.

SUMMARY OF THE INVENTION

The present invention provides overvoltage circuit protection.Specifically, the present invention provides a voltage variable material(“VVM”) that includes an insulative binder that in one embodiment isformulated to intrinsically adhere to conductive and non-conductivesurfaces. The binder and thus the VVM is self-curable and may be appliedto an application in the form of an ink, which dries in a final form foruse. The binder eliminates the need to place the VVM in a separatedevice and for separate printed circuit board pads on which toelectrically connect the VVM. The binder and thus the VVM can bedirectly applied to many different types of substrates, such as a rigidFR-4 laminate, a polyimide, a polymer, glass and ceramic. The VVM canalso be applied directly to different types of substrates that areplaced inside a piece of electrical equipment (e.g., a connector).

The binder of the VVM includes a polymer, such as polyester, which isdissolved in a solvent. One suitable solvent for dissolving the polymeris diethylene glycol monoethyl ether acetate, referred to as “carbitolacetate.” In an embodiment, a thickening agent, such as a fumed silica,is added to the insulative binder, which increases the viscosity of theinsulative binder. A number of different types of particles are thenmixed in the binder to produce a desired clamping voltage and responsetime. The different types of particles include: conductive particles(including core and shell conductive particles), insulating particles,semiconductive particles, doped semiconductive particles (including coreand shell doped semiconductive particles) and any combination thereof.

The conductive particles in an embodiment include an inner core and anouter shell. The core and the shell have different conductivities orresistivities. Either the shell is more conductive than the core or thecore is more conductive than the shell. The core and shell can eachindividually be of any of the different types of particles listed above.In one embodiment, the conductive particles include an aluminum core andan aluminum oxide shell. In another embodiment, the conductive particlesinclude a copper core and a copper oxide shell. In an alternativeembodiment, the conductive particles do not include a shell or coating.Here, conductive particles can consist substantially of a singlematerial.

In one preferred embodiment, the VVM includes conductive particles anddoped semiconductive particles. The conductive particles can besubstantially pure nickel particles, while the doped semiconductiveparticles include doped silicon. Another preferred VVM of the presentinvention includes one or more types of conductive particles mixed in aninsulating binder. In one embodiment, core-shell conductive particlesare combined with a substantially pure conductive particle in theinsulative binder. The pure conductive particle can be agglomerated orformed from multiple smaller particles to produce an overall largerparticle, such as an agglomerated tungsten particle. The core-shellconductive particles in one embodiment include an aluminum or coppercore and an insulative oxide shell. In another embodiment, a single typeof conductive core-shell particle is placed in the binder. In a furtheralternative embodiment, core-shell semiconductive particles areprovided, e.g., with a silicon core and an insulative shell, such as asilicon dioxide, epitaxial silicon or glass shell. The differentformulations provide VVM's having different clamping voltages.

The VVM having the binder of the present invention can be applied to asubstrate to form various circuits or applications. In a firstapplication, a plurality of electrodes or conductors are secured to aprinted circuit board via any known technique. The electrodes are eachseparated on the printed circuit board by a gap. The VVM is applied toand intrinsically adheres to the electrodes and the substrate in thegap. In a second application, the electrodes are again secured to thesubstrate, but the VVM only intrinsically adheres to the electrodes.That is, the VVM does not adhere to the substrate but is placed acrossthe gap.

In a third application, the VVM intrinsically adheres to a substrate,wherein the electrodes are placed on and intrinsically adhere to theVVM. That is, the VVM secures the electrodes to the substrate. In aforth application, at least one of a plurality of electrodes is securedto the substrate, wherein the VVM intrinsically adheres to the securedelectrode. At least one other electrode resides on top of the VVM. Thegap between the electrodes is formed by the thickness of the VVM. Here,the VVM may or may not additionally, intrinsically secure to thesubstrate. The electrode that resides on top of the VVM can also have aportion that secures to the substrate.

When the VVM is applied to a circuit, such as on a printed circuitboard, the quantity of VVM self-cures in a finished form that does notrequire a separate protective covering. The VVM may be left open to theenvironment through manufacture, shipping and use. The substrate can beany type of substrate, such as a rigid laminate (e.g., FR-4) used withprinted circuit boards, a material such as a polyimide used withflexible circuits (e.g., Kapton®), a polymer, ceramic or glass as wellas any combination of these.

In another embodiment, the substrate can be coated or otherwiseprotected. For example, any of the applications described above can becovered with a coating. The coating can be any one of a variety ofdifferent materials including: a dry film photo-imageable coverlay, aspray liquid photo-imageable coverlay or a “glob-top” type coating as itis known in the art. Alternatively, any of the applications describedabove can be embedded in a multilayered printed circuit board (“PCB”).In another embodiment, at least one additional electrode or conductorsecures to an underside of an upper substrate, wherein the VVM existsbetween the upper and lower substrates and intrinsically adheres to atleast the upper and lower electrodes and possibly to one or more of theupper and lower substrates.

The circuit may or may not be provided in a device. For example, thedevice in an embodiment is a telecommunications device, such as an RJ-45or RJ-11 connector. In another embodiment, the device is an input/outputconnector, such as a Deutsches Institut für Normung eV (“DIN”) connectoror ribbon cable connector. In each of these devices, the VVM protectsone or more signal lines from transient voltage spikes by connecting thesignal conductors to a ground conductor or shield.

In one embodiment, an RJ type connector includes a plurality of signalconductors. The connector also includes a grounded conductive shield.The shield is cut or stamped to yield at least one tab that is biaseddownwards towards the conductors. In one embodiment, the shield definesa separate tab for each of the conductors. The connector includes ahousing that compresses the tabs onto the conductors. VVM is appliedbetween the shield tabs and the conductors to provide overvoltageprotection to the RJ connector. In an embodiment, the VVM is theintrinsically securing VVM described above, however, a known VVMprovided in a device could also be used. In another embodiment, acapacitor is placed between the VVM and one of the conductors and theshield tab to block high DC voltages, such as those imposed during highpotential [HI-POT] testing.

The present invention also includes multiple embodiments for providing amultilayer printed circuit board having VVM protection on one or morelayers. In one embodiment, the VVM is screen-printed, stencil-printed orapplied directly via a dispenser, e.g., from a pick and place machine,into a gap between electrodes on a layer of the PCB so that the VVM issubstantially flush with the tops of the electrodes. The VVM thereforecontacts the sides or edges but not the tops (substantially) of theelectrodes. That efficient use of VVM enables an insulating layer to beapplied to the electrodes and the VVM areas, so that further electrodesand VVM areas can be applied to the second insulating layer and so on.In an alternative embodiment, the VVM extends above the thickness of theelectrodes slightly or more than slightly. Here, the VVM can contact thetops of the electrodes to a greater degree.

The multilayer PCBs can include different types of insulating materials,such as FR-4, ceramic, epoxy resin, resin coated foil, teflon, polyimideand glass. In an alternative embodiment, the VVM is dispensed directlyfrom a dispenser into the gaps defined between electrodes. The dispenseris pressurized, e.g., mechanically or pneumatically. The VVM in oneembodiment is made to have the consistency of an ink, wherein thedispenser is an atomizer that sprays the VVM between the gaps asdesired.

The VVM of the present invention is also well suited to protect newdigital cables or circuits, such as high-definition, multimediainterface (“HDMI”) circuits, cables and connectors. The HDMI circuitscan be protected in a planer X-Y type of application or via a Zdirectional structure described below.

It is therefore an advantage of the present invention to provide anintrinsically adhesive VVM.

Another advantage of the present invention is to provide a VVM that doesnot need to be housed in a separate device.

A further advantage of the present invention is to provide a VVM that isself-curing.

Yet another advantage of the present invention is to provide a VVM thatadheres directly to a printed circuit board without the need forproviding separate electrical pads on the substrate on which to mountthe VVM.

Yet a further advantage of the present invention is to provide a VVMthat adheres directly to a polymer or plastic.

Still another advantage of the present invention is to apply a VVM to asubstrate directly, wherein the substrate is provided in an electricaldevice, such as a piece of equipment or a connector.

Still a further advantage of the present invention is to provide RJ typeconnectors having overvoltage protection.

Moreover, an advantage of the present invention is to provideinput/output connectors having overvoltage protection.

Further still, an advantage of the present invention is to provide anapparatus for electrically connecting VVM (and alternatively,additionally a capacitor) to a plurality of different signal lines in anRJ type connector.

Moreover, an advantage of the present invention is, via the eliminationof the need for a housing, to provide a lower cost, readily producedcircuit protection material that can result in improved electricalperformance due to the reduction of parasitic impedance.

Still a further advantage of the present invention is to providedifferent types of VVM's and different types of particles used in theVVM's, which can formulated to provide a desired, e.g., relatively lowor high, clamping voltage.

Additional features and advantages of the present invention will bedescribed in, and apparent from, the following Detailed Description ofthe Preferred Embodiments and the Drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a typical waveform of anelectrical overstress transient.

FIG. 2 is a schematic illustration of certain possible components forthe voltage variable material (“VVM”) of the present invention.

FIG. 3A is a sectional schematic illustration of a core and shell dopedsemiconductive particle used with the VVM of the present invention.

FIG. 3B is a sectional schematic illustration of a core and shellconductive particle of the VVM of the present invention.

FIG. 3C is a sectional schematic illustration of an agglomeratedconductive particle of the VVM of the present invention.

FIG. 3D is a sectional schematic illustration of a core and shellsemiconductive particle of the VVM of the present invention.

FIG. 4 is a perspective view of a rigid printed circuit board (“PCB”)substrate that illustrates one circuit arrangement for the intrinsicallyadhesive VVM of the present invention.

FIG. 5A is a perspective view of a flexible substrate having theintrinsically adhesive VVM of the present invention.

FIG. 5B is top view of one embodiment for a high-definition multimediainterface (“HDMI”) circuit that is protected with a device containingthe VVM of the present invention.

FIG. 5C is a sectioned elevation view of another embodiment for ahigh-definition multimedia interface (“HDMI”) circuit protected with theVVM of the present invention.

FIG. 6 is a sectioned elevation view illustrating three additionalcircuit arrangements for the intrinsically adhesive VVM of the presentinvention.

FIG. 7 is a sectioned elevation view illustrating two “Z” direction typecircuit arrangements for the intrinsically adhesive VVM of the presentinvention.

FIG. 8 is a sectioned elevation view illustrating still a furthercircuit arrangement for the intrinsically adhesive VVM of the presentinvention.

FIG. 9A is a sectioned elevation view illustrating the circuitarrangements of FIGS. 4, 6 and 7 laminated in a multilayer PCB.

FIG. 9B is a sectioned elevation view illustrating another embodimentfor providing the VVM of the present invention in a multilayer PCB.

FIG. 10 is a sectioned elevation view illustrating the circuitarrangements of FIGS. 4, 6 and 7 covered with a protective coating.

FIG. 11 is a perspective view of one embodiment of a DIN connectorhaving the directly applied VVM of the present invention.

FIG. 12 is a perspective view of one embodiment of a ribbon cableconnector having the directly applied VVM of the present invention.

FIG. 13 is a cutaway perspective view of one embodiment of adata/telecommunications RJ type connector having the directly appliedVVM of the present invention.

FIG. 14 is a cutaway perspective view of a number of signal conductorsand a shield of one embodiment of a data/telecommunications RJ typeconnector having the directly applied VVM of the present invention.

FIG. 15 is a side elevation view of a signal conductor, a shield and acapacitor of one embodiment of a data/telecommunications RJ typeconnector having the directly applied VVM of the present invention.

FIGS. 16 and 17 are schematic views of various fluidized bed plasmareactors of the present invention suitable for use to coat particles ofthe voltage variable materials described herein.

FIG. 18 is a side elevation view of a screen or stencil printingapplication of the VVM of the present invention into gaps betweenconductors on an insulating layer of a PCB.

FIG. 19 is a side elevation view of one embodiment for directlydepositing the VVM of the present invention into gaps between conductorson an insulating layer of a PCB.

FIG. 20 is a schematic perspective view of another embodiment fordirectly depositing the VVM of the present invention into gaps betweenconductors on an insulating layer of a PCB, which uses a pick and placeapparatus.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 2, a voltage variable material (“VVM”) 100 of thepresent invention includes an insulative binder 50. The binder 50secures one or more or all of certain different types of particles, suchas insulating particles 60, semiconductive particles 70, dopedsemiconductive particles 80, conductive particles 90 and variouscombinations of these. The insulative binder 50 has intrinsicallyadhesive properties and self-adheres to surfaces, such as a conductive,metal surface or a non-conductive, insulative surface. The insulativebinder 50 has a property of being self-curing, so that the VVM 100 canbe applied to a circuit or application and be used thereafter withoutheating or otherwise curing the VVM 100 and the insulative binder 50. Itshould be appreciated, however, that the circuit or applicationemploying the VVM 100 with the binder 50 may be heated or cured toaccelerate the curing process.

Insulative Binder

The insulative binder 50 of the VVM 100 in an embodiment includes apolymer or thermoplastic resin, such as polyester, which is dissolved ina solvent. In one embodiment, the polyester resin has a glass transitiontemperature in the range of 6° C. to 80° C. and a molecular weightbetween 15,000 and 23,000 atomic mass units (“AMU's”). One suitablesolvent for dissolving the polymer is diethylene glycol monoethyl etheracetate, referred to as “carbitol acetate.” In an embodiment, athickening agent is added to the insulative binder 50, which increasesthe viscosity of the insulative binder 50. For example, the thickeningagent can be a fumed silica, such as that found under the trade nameCab-o-Sil TS-720.

The insulative binder 50 in an embodiment has a high dielectricbreakdown strength, a high electrical resistivity and high trackingresistance. The insulative binder 50 provides and maintains sufficientinterparticle spacing between the other possible components of VVM 100,such as the conductive particles 90, the insulating particles 60, thesemiconductive particles 70 and the doped semiconductive particles 80.The interparticle spacing provides a high resistance. The resistivityand dielectric strength of the insulative binder 50 also affects thehigh resistance state. In an embodiment, the insulative binder 50 has avolume resistivity of at least 10⁹ ohm-cm. It is possible to blenddifferent polymers in the binder 50 and to cross-link same.

Insulative binder 50 in one embodiment is intrinsically adhesive. WhenVVM 100 employs the intrinsically adhesive insulative binder 50, the VVMmay be self-cured or self-secured to conductive and insulativematerials. The intrinsically adhesive insulative binder 50 adheres andcures to any type of electrical lead, coil, electrode, pin, trace, etc.The intrinsically adhesive insulative binder 50 adheres and cures to anytype of insulative material, laminate or substrate. For example, theintrinsically adhesive insulative binder 50 adheres and cures to anytype of printed circuit board material, flexible circuit material,polymer, glass and ceramic.

In one embodiment, the intrinsically adhesive insulative binder 50 ofthe VVM 100 adheres and cures to a known FR-4 laminate. The FR-4laminate typically includes a woven or non-woven fabric, which is meshedor perforated. The intrinsically adhesive binder 50 of the VVM 100 mayalso adhere to a FR-4 layer of a multilayer PCB. In another embodiment,the intrinsically adhesive insulative binder 50 of the VVM 100 adheresand cures to a polyimide material. One type of polyimide material towhich the insulative binder 50 intrinsically secures is manufactured byDupont Corporation and is called “Kapton.” There are three variants ofthe Kapton® material. One Kapton® material includes an acrylic baseadhesive but is not flame retardant. Another Kapton® material includesan acrylic base adhesive and is flame retardant. A third Kapton®material is not adhesive. The insulative binder 50 of the VVM 100 canadhere and cure to each of the variants.

The insulative intrinsically adhesive binder 50 of the VVM 100 canfurther adhere to a rigid-flexible material. As its name implies, therigid-flexible material is a composite of two different materials, oneflexible (such as Pyralux), and the other rigid FR-4. This type ofmaterial is especially useful for any application that requiresconnection to moving or bending parts and also requires a stableplatform for components.

It should be appreciated that the insulative binder 50 for thecompositions described below does not have to be intrinsically adhesiveor self-curing. Further, in one embodiment, binder 50 includes silicone.

Insulating Particles

In an embodiment, insulating particles 60 are dispersed into the binder50 of the VVM 100. The insulating particles 60 in an embodiment have anaverage particle size in a range of about 200 to about 1000 Angstroms(“Å”) and a bulk conductivity of less than 10⁻⁶ (ohm-cm)⁻¹. In oneembodiment, the insulating particles 60 have an average particle size ina range of about 50 Å to about 200 Å.

The fumed silica of the insulating binder 50, such as that availableunder the trade name Cab-o-Sil TS-720, constitutes an insulatingparticle 60. Other insulative particles, however, can be used inaddition to the fumed silica. For example, glass spheres, calciumcarbonate, calcium sulfate, barium sulfate, aluminum trihydrate, kaolinand kaolinite, ultra high-density polyethlene (“UHDPE”) and metal oxidessuch as titanium dioxide may also be used as insulating particles 60 inthe present invention. For example, titanium dioxide having an averageparticle size from about 300 to 400 Å, manufactured by NanophaseTechnologies, provides a suitable insulating particle 60.

The insulating particles 60 can also include oxides of iron, aluminum,zinc, titanium, copper and clay such as a montmorillonite type producedby Nanocor, Inc. Insulating particles 60 in addition to the fumedsilica, if employed in the VVM 100, are present in an embodiment fromabout one to about fifteen percent by weight of the VVM 100.

Semiconductive Particles and Doped Semiconductive Particles In anembodiment, semiconductive particles 70 are dispersed into the binder 50of the VVM 100. The semiconductive particles 70 in an embodiment includean average particle size of less than 5 microns and bulk conductivitiesin the range of 10 to 10⁻⁶ (ohm-cm)⁻¹. In order to maximize particlepacking density and obtain optimum clamping voltages and switchingcharacteristics, the average particle size of the semiconductiveparticles 70 in one preferred embodiment is in a range of about 3 toabout 5 microns, or even less than 1 micron. Semiconductive particlesizes down to the 100-nanometer range and less are also suitable for usein the present invention.

The material of the semiconductive particles 70 in an embodimentincludes silicon carbide. The semiconductive particle materials can alsoinclude: oxides of bismuth, copper, zinc, calcium, vanadium, iron,magnesium, calcium and titanium; carbides of silicon, aluminum,chromium, titanium, molybdenum, beryllium, boron, tungsten and vanadium;sulfides of cadmium, zinc, lead, molybdenum, and silver; nitrides suchas boron nitride, silicon nitride and aluminum nitride; barium titanateand iron titanate; suicides of molybdenum and chromium; and borides ofchromium, molybdenum, niobium and tungsten.

In an embodiment, the semiconductive particles 70 include siliconcarbide for example, manufactured by Agsco, which can be of #1200 gritand have an average particle size of approximately 3 microns. Thesilicon carbide can alternatively be manufactured by Norton, be of#10,000 grit, and have an average particle size of approximately 0.3microns. In another embodiment, the semiconductive particles 70 includesilicon carbide and/or at least one other material including: bariumtitanate, boron nitride, boron phosphide, cadmium phosphide, cadmiumsulfide, gallium nitride, gallium phosphide, germanium, indiumphosphide, magnesium oxide, silicon, zinc oxide, and zinc sulfide.

In an embodiment, doped semiconductive particles 80 are dispersed intothe binder 50 of the VVM 100. The addition of certain impurities(dopants) affects the electrical conductivity of a semiconductor. Theimpurity or material used to dope the semiconductive material may beeither an electron donor or an electron acceptor. In either case, theimpurity occupies the energy level within the energy band gap of anotherwise pure semiconductor. By increasing or decreasing the impurityconcentration in a doped semiconductor, the electrical conductivity ofthe material is varied. The electrical conductivity of a puresemiconductor may be extended upward (into the range of a semimetal ormetal) by increasing the conduction electron concentration, or may beextended downward (into the range of an insulator) by decreasing theconduction electron concentration.

In one embodiment, the semiconductive particles 70 and dopedsemiconductive particles 80 are mixed into the insulative binder 50 ofthe VVM 100 via standard mixing techniques. In another embodiment,various different doped semiconductive particles 80 that have been dopedto different electrical conductivities are dispersed into the insulativebinder 50 of the VVM 100. Either of these embodiments can also includeinsulating particles 60.

In one embodiment, the VVM 100 employs a semiconductive particle dopedwith a material to render it electrically conductive. The dopedsemiconductive particles 80 may be comprised of any conventionalsemiconductive material including: boron nitride, boron phosphide,cadmium phosphide, cadmium sulfide, gallium nitride, gallium phosphide,germanium, indium phosphide, silicon, silicon carbide, zinc oxide, zincsulfide as well as electrically conducting polymers, such as polypyroleor polyaniline. These materials are doped with suitable electron donorsfor example, phosphorous, arsenic, or antimony or electron acceptors,such as iron, aluminum, boron, or gallium, to achieve a desired level ofelectrical conductivity.

In an embodiment, the doped semiconductive particles 80 include asilicon powder doped with aluminum (approximately 0.5% by weight of thedoped semiconductive particle 80) to render it electrically conductive.Such a material is marketed by Atlantic Equipment Engineers under thetrade name Si-100-F. In another embodiment, the doped semiconductiveparticles include an antimony doped tin oxide marketed under the tradename Zelec 3010-XC.

In an embodiment, the doped semiconductive particles 80 of the VVM 100have an average particle size less than 10 microns. In order to maximizeparticle-packing density and obtain optimum clamping voltages andswitching characteristics, however, the average particle size of thesemiconductive particles may be in a range of about 1 to about 5microns, or even less than 1 micron.

One Preferred VVM Component

One preferred doped semiconductive particle 80 is illustrated in FIG.3A. Semiconductive particle 80 includes an inner core 82 that is dopedwith at least one dopant 84. The inner core is then surrounded by anouter shell or coating 86. In one embodiment, the core material 82includes particle or powdered silicon. The silicon 82 is doped to a lowresistivity value (e.g., below 1 ohm-cm) and thereafter ground to apowder. The average size of the particles 82 is any suitable size and inone embodiment, the core particles are each between five and 100microns. In one embodiment, the average thickness of the shell orcoating is about 100 to about 10,000 Å.

The core material 82 or silicon is doped with a suitable dopant, such asantimony, arsenic, phosphorus, boron or any of the other dopants listedherein. Core material 82 can be any suitable semiconductive material,such as silicon carbide, germanium, gallium arsenide and the like. Inone embodiment, only a single type of dopant is used. It should beappreciated, however, that different types of dopants could be used inthe same particle.

The shell or coating 86 of doped semiconductive particle 80 can be madeof a multitude of different materials. For example, the coatings can beany one of the following materials: silicon dioxide, epitaxial siliconor glass. Each of those materials is inert, so that they do not reactwith other components of the VVM of the present invention.

The type of coating or shell 86 dictates the process used for formingthe coating or shell. For example, if the coating or shell 86 is anoxide, e.g., silicon dioxide, the layer is grown via heating at one ormore temperatures over a specified or variable time in one embodiment.It has been found that suitable silicon oxide layers can be formed bysubjecting the core doped silicon particles 82 to heat and temperature.In particular, the particles can be heated at a temperature of about500° C. to about 1500° C. over an oxidation time from about 15 minutesto about three hours. The heating is performed over multiple intervalsof heating and cooling. In one embodiment, the cooling is performedwhile subjecting the particles to a vacuum of about ten to 100millitorr. Vacuum cooling is advantageous because it tends to preventexposure of the VVM to moisture. The particles in one embodiment areheated for about thirty minutes and then vacuum cooled overnight. Thatprocess is then repeated.

Referring now to FIGS. 16 and 17, another method and apparatuscontemplated by the present invention for forming the coating 86 on thecore particle 82 is illustrated by a fluidized bed plasma reactor 250(FIG. 16) and a reactor 300 (FIG. 17). Fluidized bed reactor 250 isshown schematically for ease of illustration. Reactor 250 includes ahousing 252 and base 254. Housing 252 and base 254 are made of anelectrically insulative or dielectric material, such as glass orplastic, in one embodiment.

Housing 252 attaches to or defines an inlet pressure port 256 and anoutlet vacuum port 258 as illustrated. Inlet pressure port 256 extendsto a pressure chamber 260. Pressure chamber 260 defines or includes apressure plenum 262. Pressure plenum 262 enables a reactant gas fromport 256 to enter and stabilize under pressure within plenum 262.Reactant gas entering the inside of housing 252 through plenum 262 isremoved under negative pressure from port 258 defined by or attached tohousing 252.

Chamber 260 also defines or includes a bed 264 for holding coreparticles 82, such as doped core particles. The bottom wall 266 of bed264 is also the top wall of plenum 262. Wall 266 defines perforated orsintered openings 268 that enable the pressurized reactant gas to escapethrough wall 266 in a relatively uniform, steady and consistent manner.If the pressure within plenum 262 is sufficient, the gas flow throughparticles 82 will cause the particles to become entrained in the gas.The particles are thereafter held in a liquid-like state, wherein thetop of the suspension of particles 82 is relatively flat due to gravity,as would be the case if liquid were poured into bed 264. Energizedconductor 274 in combination with grounded conductor 260 creates plasmasheeting regions 276 and 278, as well as a glow discharge region 280located between plasma sheeting regions 276 and 278. Particles 82suspended in the gas stream are thereby ensured to be mixed properlywith the plasma glow discharge 280.

The reactant gas entering port 256 is carried via a carrier gas, such asnitrogen, argon, helium, carbon dioxide, oxygen, other gases andcombinations thereof. The reactant gas can be any suitable plasma gasknown to those of skill in the art, such as triethylaluminum (“TEAL”),carbon tetrachloride, Silane, Diborane and any combination thereof.

The reactor 250 is also coupled to a high frequency power supply 270that operates through a matching network 272 to supply power to a pairof electrodes 274 and 260. Matching network 272 matches the impedancesof the power supply and the reactor chamber to provide for an optimaltransfer of energy to the chamber. It should be noted that pressurechamber 260, and in particular plate 266, function additionally as asecond electrode in combination with electrode 274. Pressurized chamber260 is therefore made of a conductive material.

Power supply 270 is a high frequency power supply and is an inductivelycoupled radio frequency (“RF”) power supply in one embodiment. The highfrequency energy from supply 270 excites the reactant gas moleculesentering housing 252 through plenum wall 266, causing the molecules tobecome ionized. The fluidized bed continuously mixes the particles asdescribed above with the ionized gas so that the reaction of the coreparticles is uniform.

In one embodiment, reactor 250 is used to provide the oxide layer on thedoped core silicon 82 particles described above. The time that the dopedcore particles spend in the chamber, the amount and frequency of powersupplied to the electrodes 274 and 260 and the gases selected allcontrol the oxide growth rate and amount. It should be appreciated,however, that reactor 250 can be used to create other coatings or shellsfor particle 80 other than oxide shells. For example, the system couldbe used to apply different types of coatings with plasma-enhancedchemical vapor deposition (“PECVD”).

It should be appreciated that while reactor 250 is used in one preferredembodiment to apply an oxide layer or other coating to dopedsemiconductive core 82, the apparatus and method can be used to applycoatings to other types of core materials, such as semiconductive corematerials without dopants, insulative materials and conductivematerials. Indeed, reactor 50 can be used to produce the core-shellconductive particle 90 described below in connection with FIG. 3B.

FIG. 17 illustrates an alternative reactor 300. Alternative reactor 300includes many of the same components herein. The same functionality asdescribed above for reactor 250. Those components are marked with thesame element numbers. Reactor 300 includes an inductive coil 302 that iswrapped about housing 252. Energy from power supply 270 is inductivelycoupled to the reactor through coil 302. The dark or sheeting regions276 and 278 occur along the sides of alternative reactor 300, and theglow discharge region 280 is located between plasma sheeting regions 276and 278. Again, the gas stream entraining particles 82 ensures theproper mixing of the particles with the plasma glow discharge 280.

Each of the insulating particles 60, semiconductive particles 70 anddoped semiconductive particles 80 are optionally dispersed into thebinder 50 of the VVM 100. The fumed silica, or Cab-o-Sil, of the binder50 constitutes an insulating particle 60. In a preferred embodiment, theVVM 100 includes conductive particles 90. The conductive particles 90 inan embodiment have bulk conductivities of greater than 10 (ohm-cm)⁻¹ andespecially greater than 100 (ohm-cm)⁻¹. It is possible, however, that byusing doped semiconductive particles the VVM 100 does not includeconductive particles 90.

Conductive Particles

The conductive particles 90 in an embodiment have a maximum averageparticle size less than 60 microns. In an embodiment, ninety-fivepercent of the conductive particles 90 have diameters no larger than 20microns. In another embodiment, one hundred percent the conductiveparticles 90 are less than 10 microns in diameter. In a furtherembodiment, conductive particles 90 with average particle sizes in thesubmicron range, for example one micron down to nanometers, are used.

Suitable materials for the conductive particles 90 of the VVM 100include: aluminum, brass, carbon black, copper, graphite, gold, iron,nickel, silver, stainless steel, tin, zinc and alloys thereof as well asother metal alloys. In addition, intrinsically conducting polymerpowders, such as polypyrrole or polyaniline may also be employed, aslong as they exhibit stable electrical properties.

In an embodiment, the conductive particles 90 include nickelmanufactured by Atlantic Equipment Engineering and marketed under thetrade name Ni-120, which have an average particle size in the range of10-30 microns. In another embodiment, the conductive particles 90include aluminum and have an average particle size in the range of 1 to30 microns.

The conductive particles 90 in one embodiment are not coated and consistessentially of a single material. Referring to FIG. 3B, in anotherembodiment, the conductive particles include an inner core 92 surroundedby an outer shell 94. The core 92 and the shell 94 of the particles 90have different electrical conductivities. In an embodiment, the core andthe shell particles 90 are substantially spherical in shape and rangefrom about 25 to about 50 microns.

In one embodiment, the inner core 92 of the conductive particles 90includes an electrically insulating material, wherein the outer shell 94includes one of the following materials: (i) a conductor; (ii) a dopedsemiconductor; or (iii) a semiconductor. In another embodiment, theinner core 92 of the conductive particles 90 includes a semiconductivematerial, wherein the outer shell 94 includes one of the followingmaterials: (i) a conductor; (ii) a doped semiconductor; or (iii) asemiconductive material other than the semiconductive material of theinner core. In a further embodiment, the inner core 92 includes aconductive material, wherein the outer shell 94 may be comprised of oneof the following materials: (i) an insulating material; (ii) asemiconductor; (iii) a doped semiconductor; or (iv) a conductivematerial other than the conductive material of the inner core.

Conductive materials suitable for use in the conductive core-shellparticles 90 include the following metals and alloys thereof: aluminum,copper, gold, nickel, palladium, platinum, silver, titanium and zinc.Carbon black may also be used as a conductive material in the VVM 100.The insulating materials 60, semiconductive particles 70 and dopedsemiconductive particles 80 described above may be mixed with theconductive core-shell particles 90 in the binder 50 of the VVM 100 ofpresent invention.

In one embodiment, the core-shell particles 90 include an aluminum core92 and an aluminum oxide shell 94. In another embodiment, the core-shellparticles 90 include a copper core 92 and a copper oxide shell 94. Theparticles 90 having the aluminum or copper core 92 and the aluminumoxide or copper oxide shell 94 can then be provided in the intrinsicallyadhesive binder having formed silica with or without additional one ormore of insulating particles 60, semiconductive particles 70 or dopedsemiconductive particles 80.

In another embodiment, the core-shell particles 90 include a titaniumdioxide (insulator) core 92 and an antimony doped tin oxide (dopedsemiconductive) shell 94. These latter particles are marketed under thetrade name Zelec 1410-T. Another suitable core-shell particle 90 ismarketed under the trade name Zelec 1610-S and includes a hollow silica(insulator) core 92 and an antimony doped tin oxide (dopedsemiconductive) shell 94.

Particles having a fly ash (insulator) core 92 and a nickel (conductor)shell 94, and particles having a nickel (conductor) core 92 and silver(conductor) shell 94 are marketed by Novamet are also suitable for usein the present invention. Another suitable alternative is marketed underthe trade name Vistamer Ti-9115 by Composite Particles, Inc. ofAllentown, Pa. These conductive core-shell particles have an insulativeshell 92 of ultra high-density polyethylene (“UHDPE”) and a conductivecore 94 material of titanium carbide (“TiC”). Also, particles 90 havinga carbon black (conductor) core 92 and a polyaniline (dopedsemiconductive) shell 94 marketed by Martek Corporation under the tradename Eeonyx F-40-10DG may be used in the VVM 100 of the presentinvention.

VVM Formulations

In one embodiment of the VVM 100, the intrinsically adhesive insulativebinder 50 constitutes from about 20 to about 60%, and more specificallyfrom about 25 to about 50%, by weight of the total composition. Theconductive particles 90 in an embodiment constitute from about 5 toabout 80%, and more specifically from about 50 to about 70%, by weightof the total composition. These ranges apply whether or not VVM 100includes additional insulative particles 60, semiconductive particles 70and/or doped semiconductive particles 80. The semiconductive particles70, if present, constitute from about 2 to about 60%, and morespecifically from about 2 to about 10%, by weight of the totalcomposition.

In another embodiment of the VVM 100, the intrinsically adhesiveinsulative binder 50 constitutes from about 30 to about 65%, and morespecifically from about 35 to about 50%, by volume of the totalcomposition. The doped semiconductive particles 80 constitute from about10 to about 60%, and more specifically from about 15 to about 50%, byvolume of the total composition. The semiconductive particles 70constitute from about 5 to about 45%, and more specifically from about10 to about 40%, by volume of the total composition. The insulatingparticles 60 comprise from about 1 to about 15%, and more specificallyfrom about 2 to about 10%, by volume of the total composition.

The switching characteristics of the VVM 100 are determined by thenature of the insulating, semiconductive, doped semiconductive andconductive particles, the particle sizes and size distribution, and theinterparticle spacing. The interparticle spacing depends upon thepercent loading of the insulating, semiconductive, doped semiconductiveand conductive particles and on their size and size distribution. In thecompositions of the present invention, interparticle spacing will begenerally greater than 1,000 Å.

Through the use of the VVM 100 employing the intrinsically adhesiveinsulative binder 50 and the other particles described above,compositions of the present invention generally can be tailored toprovide a range of clamping voltages from about 30 volts to greater than2,000 volts. Certain embodiments of the present invention for circuitboard level protection exhibit clamping voltages in a range of 100 to200 volts, more specifically less than 100 volts, still morespecifically less than 50 volts, and especially exhibit clampingvoltages in a range of about 25 to about 50 volts.

One Preferred VVM

The doped semiconductive core-shell particle 80 illustrated in FIG. 3Acan be combined with many different types of particles to producedifferent voltage variable materials that suitably combat EOStransients. In one embodiment, the particles 80 of FIG. 3A are mixed inan insulative binder, such as binder 50 described above with any of theconductive particles 90 described herein. In one embodiment, conductiveparticles 90 include a substantially pure material, such as pure nickel,that is substantially not oxidized. It should be appreciated, however,that the particle 80 of FIG. 3A can be used with a core-shell-typeconductive particle described above in connection with FIG. 3B. Further,particles 80 illustrated in connection with FIG. 3A can be combined withone or more of non-doped semiconductive particles 70, conductiveparticles 90 and insulative particles 60. In one embodiment, ananotungsten powder is also added.

In one preferred embodiment, VVM 100 is formed using particles 80described in connection with FIG. 3A in combination with nickel, whereinthe doped semiconductive particles are provided in a concentration ofabout 40 to about 80% by volume, while the nickel particles are providedin a concentration of about 5 to about 25% by volume. The listedconcentrations are the resulting concentrations after VVM 100 has beencured properly via the multiple heating and cooling steps discussedabove. That is, the concentrations specify the VVM 100 as it is appliedin an application.

Particles 80 and the nickel particles are mixed in an insulative binder50, which is a polymer that is dissolved via carbitol acetate to havethe direct application properties described herein. The resulting VVM100 has a resistivity of about 1400 ohm-cm to about 14×10⁶ ohm-cm.

Another Preferred VVM

In a second preferred embodiment, VVM 100 includes two differentconductive particles that are mixed into an insulative binder 50. Thesecond preferred embodiment uses the core-shell type conductiveparticles 90 described above in connection with FIG. 3B as well asconductive particles 90 that do not have a shell, e.g., that aresubstantially not oxidized. The core-shell conductive particles 90 andthe non-oxidized or non-shell conductive particles 90 are mixed in aninsulative binder 50, which is a polymer that is dissolved via carbitolacetate to have the direct application properties described herein.

In one implementation, the core-shell particles 90 of the secondpreferred embodiment of VVM 100 include an aluminum or copper core 92and an aluminum oxide or copper oxide shell 94, although any of thecore-shell particles 90 having a core 92 and a shell 94 can be used. Thealuminum core 92 in one embodiment has an average size in the range of0.1 to 30 microns. The aluminum oxide shell 94 in one embodiment has anaverage thickness on the order of nanometers. Copper core 92 and copperoxide shell 94 can have similar sizes.

The non-oxidized or non-coated conductive particles 90 of the secondpreferred embodiment of VVM 100 can be any of the particles describedabove in connection with FIG. 2. In one implementation, as seen in FIG.3C, the non-oxidized or non-coated conductive particles 90 are tungstenparticles of about 1 to about 10 microns in average size. The tungstenparticles can be round, elongated, elliptical or ovular and in oneembodiment are agglomerated or formed from many smaller tungstenparticles 96, e.g., having average size on the order of 100 nanometers.Alternatively, the tungsten particles 90 are solid and not agglomerated.

The resulting second preferred embodiment of VVM 100 has a resistivityof about 1400 ohm-cm to about 14×10⁶ ohm-cm in one embodiment, althoughdifferent resistivities could be achieved based at least on particleloading, particle concentration and particle sizing. In one embodiment,the core-shell conductive particles 90 are provided in a concentrationof about 35% to about 80% by volume and in one implementation about52.5% by volume. The non-coated conductive particles 90 are provided ina concentration of about 2% to about 30% by volume and in oneimplementation about 17.5% by volume. The remainder of the volume isconsumed by the insulative binder 50, which can be made of any of theembodiments described above.

The second preferred VVM embodiment can but does not have toadditionally include any one or more of the insulating particles 60,semiconductive particles 70 and doped semiconductive particles 80.

A Further Preferred VVM

In a third preferred embodiment, VVM 100 includes two differentconductive particles 90 and semiconductive particles 70 that are mixedinto an insulative binder 50. The third preferred embodiment uses thecore-shell conductive particles 90 as well as non-oxidized or non-coatedconductive particles 90 that do not have a shell, e.g., that aresubstantially not oxidized, as described above in connection with thesecond preferred embodiment. The insulative binder 50 is in onepreferred implementation a polymer that is dissolved via carbitolacetate to have the direct application properties described herein.

The semiconductive particles 70 can be any such particles listed abovein connection with FIG. 2. As seen in FIG. 3D, in one preferredembodiment, the semiconductive particles 70 have a semiconductive core72 and an insulative shell 74, which can include silicon dioxide,epitaxial silicon, glass and any combination thereof. In oneimplementation, the semiconductive core 72 is made of arsenic dopedN-type silicon having an average size of about two to about 30 microns,while the insulative shell 74 is silicon dioxide having an averagethickness of on the order of nanometers.

In still a further alternative embodiment, the doped semiconductivecore-shell or non-shell doped semiconductive particles 80 describedabove are used instead of or in addition to semiconductive particles 70.Insulating particles 60 can also be used.

In one implementation, the core-shell particles 90 of the thirdpreferred embodiment of VVM 100 include an aluminum core 92 and analuminum oxide shell 94 (the same as the second preferred embodiment).Alternatively, any of the core-shell particles 90 having a core 92 and ashell 94 can be used. The aluminum core 92 in one embodiment has anaverage size in the range of 10 to 30 microns. The aluminum oxide shell94 in one embodiment has an average thickness on the order ofnanometers.

The non-oxidized or non-coated conductive particles 90 of the thirdpreferred embodiment of VVM 100 can be any of the particles describedabove in connection with the second preferred embodiment. In oneimplementation the non-oxidized or non-coated conductive particles 90are tungsten particles of about 1 to about 10 microns in average size.The tungsten particles can be round, elongated, elliptical or ovular,agglomerated or not agglomerated as described above.

The resulting third preferred embodiment of VVM 100 has a resistivity ofabout 1400 ohm-cm to about 14×10⁶ ohm-cm in one implementation, althoughdifferent resistivities could be achieved based at least on particleloading, particle concentration and particle sizing. In one embodiment,the conductive particles 90 (core-shell) are provided in a concentrationof about 15 to 45% by volume. The conductive particles 90 (non-oxidizedcore) are provided in a concentration of about 1 to 20% by volume and inone implementation about 10% by volume. The semiconductive (core-shellor non-shell) particles 70 or doped semiconductive core-shell ornon-shell particles 80 are provided in a concentration of about 15 to45% by volume and in one implementation about 30% by volume. Insulativebinder 50 consumes the remainder of the volume, which can be any of theembodiments described above.

Yet Another Preferred VVM

In a fourth preferred embodiment, VVM 100 includes only the core-shellconductive particles shown in FIG. 3B. The insulative binder 50 is inone preferred implementation a polymer that is dissolved via carbitolacetate to have the direct application properties described herein.

In one implementation, the core-shell particles 90 of the fourthpreferred embodiment of VVM 100 include an aluminum nitride core 92 anda silica shell 94. Alternatively, any of the core-shell particles 90having a core 92 and a shell 94 can be used. For example, an aluminum orcopper core 92 can be used (i) instead of or (ii) in addition to theconductive particles 90 having an aluminum nitride core 92 and a silicaor oxide shell 94. In another example, an oxide shell 94 can be used (i)instead of or (ii) in addition to the conductive particles 90 having analuminum or aluminum nitride core 92 and a silica shell 94.

The aluminum or aluminum nitride core 92 in one embodiment has anaverage size in the range of 10 to 30 microns. The aluminum oxide shell94 in one embodiment has an average thickness on the order ofnanometers. Conductive particles 90 have a bulk conductivity greaterthan 10 (ohm-cm)⁻¹ in one embodiment.

The resulting fourth preferred embodiment of VVM 100 has a resistivityof about 1400 ohm-cm to about 14×10⁶ ohm-cm in one implementation,although different resistivities could be achieved based at least onparticle loading, particle concentration and particle sizing. In oneembodiment, the core-shell conductive particles 90 are provided in aconcentration of about 35 to about 75% by volume. Insulative binder 50consumes the remainder of the volume and can be any of the embodimentsdescribed above. The resulting VVM has relatively low clamping voltageof about 65 volts to about 120 volts.

The fourth VVM 100 can alternatively or additionally includenon-oxidized or non-coated conductive particles 90, which can be any ofsuch particles described above. In one implementation the non-oxidizedor non-coated conductive particles 90 are tungsten and/or nickelparticles. The tungsten particles can be round, elongated, elliptical orovular, agglomerated or not agglomerated as described above. Thenon-oxidized or non-coated conductive particles are provided in aconcentration of about 2% to about 30% by volume.

Direct Application of VVM

Referring now to FIG. 4, one possible arrangement 115 for any of theembodiments of the intrinsically adhesive VVM 100 is illustrated. Thearrangement 115 appears in this example on substrate 110, which is arigid PCB. A number of other electrical devices 113 are illustrated,which shows that the VVM 100 is open and exposed when the PCB substrate110 is in a finished form. The electrical devices 113 include any typeof electrical device commonly connected to a PCB including boththrough-hole and surface-mounted devices. The electrical devices 113include any electrical components, such as a resistor or capacitor. Theelectrical devices 113 also include any type of integrated circuit,connector, filter, etc.

The arrangement 115 resides next to the other electrical components 113on the PCB substrate 110. The arrangement 115 is illustrated having twoelectrodes 117 and 119 that are each secured to the PCB substrate 110via any method known to those of skill in the art. Although twoelectrodes 117 and 119 are illustrated, the arrangement 115 can have anynumber of electrodes. In the arrangement 115, the quantity of VVM 100intrinsically adheres to the electrodes 117 and 119 and to the substrate110. A gap exists between the electrodes 117 and 119, which is shown inphantom in this perspective view because it is covered by the quantityof VVM 100. The gap width in an embodiment is around 2 mils, however,larger or narrower gap widths may be used. The electrodes 117 and 119normally do not electrically communicate with one another. Upon an EOStransient event, the VVM 100 switches from a high impedance state to alow impedance state, wherein a transient spike shunts, here, from theelectrode 117 through the VVM 100 to the electrode 119, which isconnected to a shield ground or earth ground as illustrated.

For convenience, the electrode 117 as illustrated terminating with afragmented end. It should be appreciated that the electrode 117 can leadto any type of electrical device. In an embodiment, electrode 117 is atrace on the PCB that carries a signal, e.g., from a telecommunicationstransmission. In this case, the electrode 117 may lead to a connectorthat receives a telecom input line or to some type of transceiver.

Referring now to FIG. 5A, a “Z” direction arrangement is illustrated ona substrate 110, which in an embodiment is a multilayered flexibleribbon or circuit. The flexible substrate 110 includes a plurality offlexible layers 111 and 112. As described above, the flexible substrate110 may include layers 111 and 112 that are made of a polyimide. Forexample, the layers 111 and 112 may be Kapton®. In another embodiment,one or both of the layers 111 and 112 are mylar layers. A section of thelayer 112 of the substrate 110 is cut away so as to illustrate a numberof signal conductors 116 as well as a ground conductor 118. With theconductors 116 and the ground conductor 118 exposed, the self-adhesiveVVM 100 having the self-curable binder 50 can be applied across each ofthe conductors 116.

As illustrated, each of the conductors 116 and the ground conductor 118is separated by a gap, so that the conductors do not normallyelectrically communicate with one another. In an embodiment, the groundconductor (only a portion shown for convenience) 118 lays on top of theVVM 100. The gap is therefore said to be in the “Z” direction, whereinthe gaps between the conductors 116 reside in an X-Y plane. Thethickness of the VVM layer is less than the spacing between signalconductors 116. An EOS transient will therefore jump from one of theconductors 116 to ground 118 instead of to another conductor 116. Inanother embodiment, a separate ground trace 118 can be placed next toeach signal trace, so that the transient will jump from a signal trace116 to a ground trace 118. Either way, the layer of VVM 100 enables anyof the signal conductors 116 that experiences an overvoltage to shuntsame to a ground conductor 118.

As in the rigid PCB application of FIG. 4, the conductors or electrodes116 (and 118) secure to a surface of a substrate. Here, conductors 116secure to an inner surface 114 of the flexible layer 111 via any methodknown to those of skill in the art. In the “Z” direction embodiment, theground conductor sticks to the top of the layer of VVM 100. Theconductors 116 and ground conductor 118 are also compressed and held inplace by the multiple layers 111 and 112. However, it is possible thatthe VVM 100 is exposed on the outside of one of the flexible layers 111and 112. The quantity of VVM 100 covers each of the conductors 116 asillustrated and also intrinsically adheres to the inner surface 114 ofthe layer 111. The layer of VVM 100 self-cures to the plurality ofconductors 116 and the inner surface 114 of the layer 111 without theneed for an additional curing or heating step. In an alternativeembodiment, however, the layer of VVM 100 may be more quickly cured byheating the flexible circuit for a predetermined amount of time.

The binder 50 as described above cures in such a manner that thequantity of VVM 100 does not crack or split even when the flexiblesubstrate 110 is bent or moved. Even so, the exposed area of innersurface 114 and the ground plane 118 in a preferred embodiment arecovered for purposes of electrical insulation. In an embodiment, the VVM100 and the conductors 116 and ground conductor 118 are covered by asilver ink coating. The VVM in an embodiment can cover an entire surfaceof the traces 116 and ground trace 118 to enhance the dissipationability of the VVM 100. In a further alternative embodiment, anintermediate insulative coating, such as a dry film photo-imagable coverlay, a spray liquid photo-imagable cover lay or a “glob-top” coating,can be disposed between the signal traces 116 and the inner surface 114of outer insulating (e.g., plastic) layer 111.

Referring now to FIG. 5B, VVM 100 of the present invention is used inconnection with a high-definition multimedia interface (“HDMI”) circuit30. VVM 100 is compatible with various types of high speed interfaces,such as Universal Serial Bus (“USB”) Rev. 2.0, FireWire and HDMI. Forease of illustration, the following description is shown in connectionwith an HDMI circuit. It should be appreciated however that theteachings with respect to the HDMI circuit also extend to other types ofhigh speed interfaces, such as those mentioned previously.

HDMI circuits or connectors are used in advanced audio/videointerfacing. Circuit 30 can interface between any HDMI-enabledaudio/video source, such as a digital video disk player, and anaudio/video receiver or an audio and/or video monitor. HDMI circuits orcables are becoming more popular due to their ability to supportstandard, enhanced or high-definition video and audio on a single lineor cable. HDMI circuit 30 in one embodiment is an all-digitalaudio/video interface. HDMI circuit 30 has a very large bandwidth, i.e.,5 Gbps, which supports current demands. For example, high definitiontelevision uses less than one-half of the available HDMI bandwidth,leaving bandwidth room to incorporate new technological advances.

In the embodiment illustrated in FIG. 5B, HDMI circuit 30 includes acable 32 that embeds a plurality of signal line pairs 34, 36, 38 and 40.Signal line pair 34 includes positive line C1+, negative line C1− and ashield line located between lines C+ and C1−. Signal line pair 36includes positive line D0+, negative line D0−, separated by a shieldline. Signal line pairs 38 and 40 follow the same format. It should beappreciated that HDMI circuit 30 can include fewer or more than foursignal line pairs.

The insulation or dielectric of cable 32 that covers signal line pairs34, 36, 38 and 40 is removed or stripped in certain places to enable aVVM-containing device 25 to be connected electrically to the signal andshield lines of pairs 34, 36, 38 and 40. Alternatively, cable 32 isfabricated to include electrodes or terminals that mate with theelectrodes or terminals of device 25.

In an alternative embodiment, device 25 is located at an end of cable 32and cooperates with an HDMI connector. In cooperating with suchconnector (e.g., one housing including both the connector apparatus andcircuit protection apparatus), the device 25 contacts the signal andshield lines that extend from the protective covering of cable 32 andinto the end terminations of the connector. Further alternatively, VVM100 is applied directly beneath the protective covering of cable 32 in amanner similar to the embodiment shown in connection with FIG. 5A. Thatalternative embodiment employs a Z-direction application. Conversely,device 25 shown in FIG. 5B employs an X-Y or planer application.

In FIG. 5B, the top of housing 22 of device 25 has been cut away toillustrate the VVM 100, a plurality of signal conductors 24 and aplurality of shield conductors 26. Shield conductors 26 each lead to acommon line that couples each of the signal conductors 26 electrically.Shield conductors 26 communicate individually with each of the shieldlines of the signal pairs 34, 36, 38 and 40 and connect those shieldlines to the common shield line.

The signal conductors 24 each extend from one of the positive andnegative signal lines of the signal line pairs 34, 36, 38 and 40 to apoint near the common shield line 26 to create a gap having a distanceX. The signal conductors 24 are also spaced apart from one another atleast a distance Y. The distance X is less than the distance Y.Accordingly, an EOS transient event occurring along any of the signallines C1+, C1−, D0+, D0−, D1+, D1−, D2+ and D2− is shunted through VVM100 to one of the shield lines 26 rather than to another signalconductor 24. VVM 100 in FIG. 5B can be any of the embodiments orformulations for the VVM discussed herein.

FIG. 5C illustrates an end view of an alternative HDMI arrangementillustrated by a device 35. The view is taken along a plane defined bydashed line VC-VC shown in FIG. 5B. Device 35 also operates as an endconnector for HDMI circuit 30. That is, device 35 can be of a male typethat receives or mates with a mating female connector via any knownconnector mating method. Alternatively, device 35 is a female connectorthat receives or mates with a mating male connector via any knownconnector mating method.

Device 35 illustrates a Z-direction VVM application for protecting anHDMI circuit 30 as opposed to the X-Y or planer application of FIG. 5B.The cable or insulation 32 of HDMI interface 30 terminates inside device35. As before, each of the signal lines C1+, C1−, D0+, D0−, D1+, D1−,D2+ and D2− communicates electrically with a signal conductor 24. Eachof the shield lines (identified by letter S) of the HDMI circuit 30communicates electrically with a shield conductor 26.

For purposes of illustration, a frame ground conductor 28 is alsoillustrated to show that in one embodiment, a transient spike is shuntedto a signal shield line rather than to frame ground 28. Signalconductors 24 and shield conductors 26 each contact an area of VVM 100.As illustrated, the distance Z from each of the signal conductors 24 tothe shield conductor 26 is less than the shortest distance Y between anytwo signal conductors 24. Accordingly, a transient spike will be shuntedfrom one of the conductors 24 to the shield conductor 26 before shuntingto another signal conductor 24.

Referring now to FIG. 6, three alternative applications 120, 125 and 130for the VVM 100 are illustrated. Each of the applications 120, 125 and130 is illustrated in a simplified form having only two conductors. Itshould be appreciated however, that any of the applications disclosedherein can electrically connect and protect a multitude of conductors,such as in FIGS. 5A to 5C. It should also be assumed, although notillustrated, that one of the conductors is a ground or shield conductor,or another type of conductor with a low impedance path to ground, whileat least one other conductor is a signal or line conductor, wherein theVVM 100 shunts and overvoltage transient from the line or signalconductor to the ground or shield conductor. Further, applications 120,125 and 130 are illustrated in a finished form, wherein VVM 100 is openand exposed to the environment.

The arrangement 120 illustrates a circuit having conductors 122 and 124that are spaced apart by a gap. Each of the conductors 122 and 124 issecured to the substrate 110 via any method known to those of skill inthe art. The substrate 110 can be any of the substrates described abovesuch as a rigid PCB substrate or a flexible circuit type of substrate.The application or circuit 120 differs from the circuit 115 in that theVVM 100 does not adhere to the substrate 110. To form such a circuit, itmay be necessary to support the VVM 100 above the gap until the VVM 100cures and dries in place. In another embodiment, a top layer or coatingmay also adhere to the VVM 100 wherein the coating enables the VVM 100in a semi-cured state to be placed on the conductors 122 and 124.Importantly, the VVM 100 does not need to adhere to the substrate 110 inthe gap area in order for the VVM 100 to function properly. The circuit120 functions exactly the same way as the circuit 115 illustrated inFIG. 4, with regard to the shunting capabilities of the VVM 100.

The circuit or arrangement 125 illustrates that the VVM 100 canintrinsically secure to the substrate 110 and thereby form a buffer orbed onto which conductors 127 and 129 are placed. The electrodes 127 and129 are separated by a gap. The electrodes may sink slightly into theVVM 100 as illustrated or the electrodes 127 and 129 may be placed ontothe VVM 100 when the VVM has cured to the point that it does not deformdue to the weight of the conductors or due to the application process.The circuit or arrangement 125 operates the same as the circuits 115 and120.

The circuit or arrangement 130 illustrates an embodiment where one ofthe conductors, namely, the conductor 132 secures to the substrate 110,while a second conductor 134 is suspended on top of the layer of VVM100, similar to the electrodes 127 and 129 of the arrangement 125. Thegap in the circuit 130 is a vertically disposed gap. The gaps in thearrangements 115, 120 and 125 are horizontally disposed. It should beappreciated that the VVM 100 operates equally as well whether the gap isan “XY” direction type of gap, such as with the arrangements 115, 120and 125, or whether the gap is a “Z” direction type of gap asillustrated in the arrangement 130.

Each of the arrangements of FIG. 6 may be desirable in certainelectrical configurations and with certain electrical components. TheVVM 100 having the insulative binder 50 of the present inventionprovides the flexibility to arrange electrodes in different ways withrespect to the substrate 110, wherein the VVM 100 does not require anextra apparatus or housing to mechanically hold the VVM or toelectrically connect it to the conductors. For example, many VVM devicesrequire a housing or shell that holds the VVM in place. Many VVM's alsoinclude a pair of terminals disposed on the housing or shell that mustbe soldered to a pair of pads formed on the surface of the substrate.From the pads, additional traces or bond wires are required to extend toconnecting signal lines or ground line.

Referring now to FIG. 7, an additional circuits or arrangements 135 and145 are illustrated. The arrangement 135 is similar to the arrangement130 in that there is a “Z” direction gap between an upper electrode 137and a lower electrode 139, wherein the lower electrode 139 is secured tothe substrate 110. In the arrangement 135, however, the upper electrode137 extends laterally or horizontally away from the lower electrode 139and turns downwardly to attach to the substrate 110. The horizontaloffset creates a second gap. When an overvoltage occurs, the transientspike may conduct through VVM 100 either in the “Z” direction or in an“XY” direction, depending on which path has the lower impedance. Thearrangement 135 otherwise operates the same as the other arrangements.

The arrangement 145 is similar to the flex circuit embodiment of FIG.5A, except the conductors 146 and 149 are disposed on rigid substrate110. In one embodiment, the floating conductor 147 is the groundconductor, making the arrangement a purely “Z” direction application. Inanother embodiment, either of the conductors 146 and 149 is the groundconductor making the application a “Z” direction and an “XY” directionapplication, wherein the voltage can discharge from one of theconductors 146 or 149, to the floating conductor 147, and down to theother conductor, which is the ground conductor.

Referring now to FIG. 8, a further alternative arrangement or circuit140 is illustrated. The circuit 140 includes two substrates 110, whichmay be a rigid substrates such as FR-4 boards, or a flexible substrates,such as a polyimide or Kapton®. A first electrode 142 is secured to theupper substrate 110, while a second electrode 143 secures to the lowersubstrate 110. The electrodes 142 and 143 are spaced apart in the “Z”direction by a quantity of VVM 100. The arrangement 140 is useful, forexample, in a flexible circuit, wherein the substrates 110 are outerlayers of Kapton® or mylar, and wherein the upper conductor 142, forexample, is a signal conductor and the lower conductor 143 is a groundconductor. Here, a multitude of signal conductors can be applied toeither the upper or lower substrates 110, wherein a transient spiketravels vertically or horizontally depending upon where the signal tracehaving the transient spike is located with respect to a groundconductor.

Referring now to FIG. 9A, the previous arrangements or circuits 115,120, 125, 130, 135 and 145 are illustrated as being imbedded inside amultilayer PCB. That is, the substrate 110 constitutes one layer of aPCB. A second substrate 144 (not to scale) constitutes another layer ofthe multilayer PCB. The layer 144 is formed around the various circuitsso as to produce a smooth outer surface that is suitable for mountingelectrical components 113 and circuit board traces. The configuration ofFIG. 9A is particularly useful in that the outer surfaces of thesubstrates 110 and 144 are not inhibited whatsoever by the circuitprotection. The embodiment illustrated in FIG. 9A can include more thantwo layers, and thus the embodiment can include a multitude of differentsubstrates having one or more of the arrangements 115, 120, 125, 130,135 and 145.

Referring now to FIG. 9B, an alternative embedded multilayer PCBapplication for VVM 100 is illustrated. The PCB can be small enough tofit inside of a device that itself is surface mounted to a larger PCB.The PCB is alternatively a larger PCB that holds potentially largecomponents, such as integrated circuits, capacitors, connectors and thelike. The PCB is alternatively a flexible circuit or cable as describedherein.

The application includes multiple insulating layers 110 a, 110 b, 110 cand 110 d. A plurality of electrodes 42 a, 42 b and 42 c are applied toinsulating layer or substrate 110 a. The electrodes 42 a, 42 b and 42 cdefine two gaps G between the electrodes. VVM 100 is placed in gaps G sothat when the multilayer PCB is completed, VVM 100 contacts the sides ofelectrodes 42 a, 42 b and 42 c but does not contact or substantiallycontact the top of electrodes 42 a through 42 c. In that manner, the VVM100 is substantially flush with the tops of electrodes 42 a to 42 c andenables a smooth upper insulating layer 110 b to be applied to (i) lowerinsulating layer 110 a, (ii) electrodes 42 a through 42 c and (iii) VVMareas 100. In alternative embodiments, shown for example in FIG. 9A, theVVM is not applied as judiciously and extends above the electrodesand/or contacts a greater portion of the tops of the electrodes.

Smooth insulating layer 110 b is capable of receiving a next layer ofelectrodes 44 a, 44 b and 44 c that define gaps G. Any of the gaps G ofFIG. 9B can be sized to be about 0.005 inch (127 microns). Theelectrodes or traces 42 a to 42 c and 44 a to 44 c are nickel platedadjacent to the gap area in one embodiment.

The application process for VVM 100 is repeated to fill the gaps Gbetween electrodes 44 a to 44 c with VVM 100 so that the VVM 100, whenthe multilayer board is completed, lies substantially flush with thetops of electrodes 44 a to 44 c. That even and flush application enablesa smooth third insulating layer 110 c to be applied to (i) electrodes 44a to 44 c, (ii) insulating layer 110 b and (iii) VVM areas 100. Thesmooth top surface of insulating layer 110 c enables another flat orfinishing insulating layer 110 d to be applied thereon.

In an embodiment, outer insulating layers 110 a and 110 d are FR-4,ceramic or other type of insulating material such as epoxy resin, resincoated foil, teflon, polyimide and glass. Alternatively, more malleableor non-rigid insulators can be used for the outer coatings 110 a and 110d. Inner insulating layers 110 b and 110 c are alternatively made of anon-rigid insulator, such as epoxy resin, a polymer insulator, a b-stagematerial (with or without copper) and the like. It should be appreciatedthat relatively rigid FR-4-type insulators can also be provided asinternal insulating layers, however, woven glass FR-4 may damage VVM 100causing resistance shifts after ESD pulsing. A non-glass insulatorshould therefore be used when contacting VVM 100. It should further beappreciated that third and fourth layers of electrodes and VVM areas 100can be provided (or any suitable number of layers according tospecification).

FIG. 9B illustrates that insulation layer 110 b resides between VVM 100and electrode or trace 44 c. In such a case, insulation layer 10 b hasto provide a minimum separation distance D between VVM 100 and electrode44 c. Minimum separation distance D ensures that a transient spike willtravel in the direction across gap G, from electrode 42 b to 42 c orvice versa instead of from electrode 42 b or 42 c in the Z direction toelectrode 44 c. The minimum separation distance D is dependent upon thedielectric strength of the insulation layer 110 b, e.g., of cured epoxyresin, and upon the maximum ESD pulse magnitude requirement. Therelationship can be expressed as follows:

Minimum Separation (D)=Maximum ESD Magnitude/Dielectric Strength

For example, if the embedded ESD device must withstand a maximum ESDpulse of 15 kV and the insulation layer 110 b, e.g., cured epoxy resin,has a dielectric strength of 150 kV/mm, the minimum separation is:15 kV/150 (kV/mm)=0.1 mm or 4 mils

The minimum separation distance D is required whether VVM 100 is made tobe substantially flush with electrodes 42 a to 42 c and 44 a to 44 c asseen in FIG. 9B or whether the VVM extends above the electrodes andperhaps contacts at least a portion of the top of the electrodes as seenin FIG. 9A for example. For example, if VVM 100 is applied so that itresides on average one mil higher than the thickness of the electrodesand the minimum separation distance D is four mils as shown above byexample, the upper Z direction electrode should reside at least fivemils above the lower electrode, at least at the point where VVM 100 isapplied.

The multilayer PCB of FIG. 9B enables circuits eventually applied to thePCB to be protected beneath the surface of the board, i.e., withoututilizing board (including flexible cabling) surface space. Certainmultilayer PCBs include circuitry and components located on the innerlayers. The embodiment of FIG. 9B illustrates one effective way forproviding circuit protection for such inner circuits and components.

Referring now to FIG. 10, a similar arrangement is illustrated havingthe circuits 115, 120, 125, 130, 135, and 145, wherein instead of thearrangements being part of a multilayer PCB, the arrangements arecovered by a protective coating 148. Even though the VVM 100self-secures to various electrodes and to the substrate 110 in certainplaces, it may also be desirable for a number of reasons to apply aprotective coating 148. For example, as with the flexible circuitillustrated in FIG. 5A, the conductors may be exposed at certain pointsand require electrical insulation. The protective coating 148 can be anytype of coating known to those of skill in the art. In an embodiment,the coating includes any of the coatings described above for theflexible circuit in FIG. 5A, such as a silver ink, a dry filmphoto-imageable cover lay, a spray liquid photo-imageable cover lay or a“glob-top” coating.

Methods of Application

The present invention provides a multitude of ways for producing the VVMcircuit board or substrate applications of FIGS. 4 through 10, and inparticular the multilayer circuit board of FIG. 9B. Referring now toFIGS. 18 to 20, certain methods are illustrated. FIG. 18 illustrates theinsulating layer 110 a and electrodes 42 a through 42 c of FIG. 9B. Ascreen, fine mesh or stencil 46 is laid over electrodes 42 a through 42c and gaps G between those electrodes. A squeegee 52, which can be madeof a rubber rod, rubber plate, flat metal or other material and shape isapplied to screen or stencil 46. The squeegee 52 includes a smooth andnon-sticking surface and a sharp printing edge. The configuration andswiping application of squeegee 52 causes VVM 100 to roll and translatealong the top of stencil 46, which helps prevent clogging of apertures48 a and 48 b, defined by stencil or screen 46. As illustrated by thearrows in FIG. 18, the horizontal action of squeegee 52 rolls VVM 100clockwise as shown in FIG. 18 and translates VVM 100 through apertures48 a and 48 b of screen 46 into the gaps G between electrodes 42 a, 42 band 42 c. To ensure an accurate print of VVM 100 into gaps G, a visionsystem can be used to detect proper alignment between screen or stencil46 and electrodes 42 a and 42 c.

As seen in FIG. 18, the newly applied VVM 100 can extend into apertures48 a and 48 b of stencil or screen 46 above the level where VVM 100would be flush with the tops of conductors 42 a and 42 b. Insulatinglayer 110 b (FIG. 9B) and its application process compress VVM 100 flushto the tops of electrodes 42 a and 42 b and fill interstices left withingaps G. Alternatively, the thickness of stencil or screen 46 is so thinthat the VVM as applied by squeegee 52 is already virtually flush withthe tops of electrodes 42 a to 42 c prior to the application of the nextinsulating layer 110 b. After insulating layer 110 b and upperelectrodes 44 a to 44 c (FIG. 9B) are applied, the screen orstencil-printing operation is performed again, and so on as many timesas necessary to produce a multilayer board of a desired number of layersand thickness.

FIG. 19 illustrates an alternative embodiment for applying the VVM 100into gaps G so that the VVM is flush or substantially flush with thetops of electrodes 42 a to 42 c. Here, a dispenser 54 is used todispense VVM 100 directly into gaps G. Dispenser 54 includes adispensing plate 56 defining apertures 58 a and 58 b. Apertures 58 a and58 b are aligned with gaps G between electrodes 42 a to 42 c so that VVM100 is placed in the desired locations. A plate is pressurized(illustrated by arrows marked P) to push VVM 100 through apertures 58 aand 58 b in plate 56 into gaps G.

Pressure P can be applied to dispenser 54 pneumatically or mechanically,e.g., via a screw conveyer. VVM 100 can alternatively or additionally beatomized or provided in the form of an ink. In such a case, plate 56provides many small holes instead of larger apertures 58 a and 58 b tospray or dispense VVM 100 into gaps G.

The processes illustrated in connection with FIGS. 18 and 19 may or maynot use an additional trimming step to trim excess VVM from electrodes42 a to 42 c and/or other areas of the printed circuit board. In oneembodiment, a laser is employed to trim the excess material fromelectrodes 42 a to 42 c, etc. It is also expressly contemplated toprovide and dispense the VVM 100 in such an efficient manner thattrimming is not necessary. The resulting application as shown above canprovide VVM protection for a plurality of electrodes and in differentareas on an insulating layer. Such protection can also occur on multipleinner layers of a multilayer PCB as well as on one or more outer layersof the PCB.

FIG. 20 illustrates an application of VVM 100 of the present inventionusing a pick and place or X-Y gantry system 240. System 240 includes abase 242 upon which an X-direction motor 244 is mounted. Motor 244 iscoupled to a high precision lead screw 246. Lead screw 246 drives anX-direction gantry 250. X-direction gantry 250 in turn supports aY-direction motor 252. Motor 252 is coupled to a second high precisionlead screw 248. Lead screw 248 drives a Y-direction gantry 254. A VVMdispenser 256 is coupled to Y-direction gantry 254 and can be moved inboth X and Y directions precisely to dispense VVM 100 selectively atdesired locations on a printed circuit board 260. Printed circuit board260 includes traces or electrodes 262 defining gaps (not illustrated)between which VVM 100 is applied as discussed above. Printed circuitboard 260 also includes other electrical devices 113 as described abovein connection with FIG. 4.

X-direction gantry 250 is balanced and supported by a shaft 258, whichis coupled to base 242 via bearings and pillow blocks 262 a and 262 b. Athird bearing 262 c and pillow block is also provided to support one endof lead screw 246. Motors 244 and 252 are highly accurate motors thatcan control precisely the location of dispenser 256 relative to PCB 260.In one embodiment, motors 244 and 252 are stepper motors that receivemotor currents from drivers that are controlled via a software program.Those components collectively control acceleration, velocity anddistance traveled, thus setting the acceleration, velocity and X-Ylocation of gantries 250 and 254 as well as dispenser 256. The motorscan also start, stop and change directions very quickly, increasingproduction speed. Lead screws 246 and 248 are sized so that dispenser256 can reach any part of PCB 260. In an alternative embodiment, linearmotors are used instead, replacing lead screws 246 and 248.

Pressurized VVM 100 is fed from a supply (not illustrated) through asupply line 264 to dispenser 256. Dispenser 256 is equipped with a valve(not illustrated) or other type of metering apparatus or dispenser thatdispenses a desired quantity of VVM 100 at a desired time and location.Trimming with a razor blade or knife may be done to remove excess VVM.The valve or metering device may be left open in certain instances wherea stream, strip, curved or oblong shaped deposit of VVM is to be formed.To that end, the pick and place or X-Y gantry system 240 enables VVM tobe applied in one or more trace-like patterns, similar to the coppertraces or electrodes. The pressurized feed of VVM through dispenser 256enables VVM 100 to be fed continuously as the dispenser is moved in twodimensions about PCB 260. The dispenser can also be stopped at certainpoints to apply more VVM at a desired location.

Devices Employing Direct VVM

Referring now to FIG. 11, the VVM 100 of the present invention may beemployed in a device. Two devices are illustrated above in connectionwith FIGS. 5B and 5C. Those devices interface with a plurality ofsubstantially parallel signal and shield conductors of an HDMI typeconnector. Another type of device illustrated in FIG. 11 includes avariety of connectors that comply with the Deutsches Institut fürNormung eV (“DIN”) standards. A circular DIN connector 150 isillustrated. It should be appreciated that the present invention may beadapted for miniature DIN connectors, double row elongated DINconnectors, shielded DIN connectors, etc. The present invention may beimplemented in a plug or receptacle. Vertical, horizontal and in-lineconnectors that attach to a cable may also be employed. Otherwise, theDIN connector may be panel mounted.

The connector 150 includes a body 152 that is constructed of anysuitable material. The body, in both plug and receptacleimplementations, secures a circular wall 154 or a plurality of straightwalls (not illustrated) that at least partially encompass a plurality ofsignal conductors 156. The conductors 156 extend from a substrate 158 ina direction that is substantially parallel with the wall 154. The wall154 and conductors 156 plug into a mating female DIN connector as iswell known.

In the illustrated embodiment, the body 152 is a plug and the conductors156 are pins. In an alternative embodiment (not illustrated), the bodyis a receptacle, and the signal conductors are sockets that receive pinsfrom a mating connector. The connector 150 may be configured so that thebody 152 secures any number of input/output conductors 156. One or moreof the outer signal conductors 156 may be a ground conductor. Normally,however, a separate (here central) ground or shield ground conductor 160is provided. In order for the illustrated embodiment to properly shunt atransient voltage spike to the ground conductor 160, the spacing betweenthe input/output conductors 156 and the ground conductor 160 should beless than the spacing between the input/output conductors 156.

In one embodiment, the substrate 158 is a PCB, such as an FR-4 board. Inanother embodiment, the substrate 158 includes another type ofinsulative material, such as a polyimide or plastic. The substrate 158fits inside the body 152 so that the connector 150 may be properlyplaced into a mating connector. In an embodiment, substrate 158 definesapertures that enable the conductors 156 to extend through from a backside of substrate 158 to the illustrated front side.

At least one quantity of VVM 100 is directly adhered or cured to thesubstrate 158. As illustrated, the VVM 100 of the present inventiondirectly connects the signal conductors 156 to the ground conductor 160without the need for traces or bond wires. In another embodiment, one ormore conductors 156 or further alternatively the ground conductor 160may contact an individual quantity of VVM 100, wherein one or moretraces or bond wires individually secure the VVM 100 to another VVMquantity or to another conductor. The traces in an embodiment are copperthat is etched onto the PCB substrate 158 as is well known. The signaltraces can communicate with either or both the single signal conductors156 and/or the ground conductor 160.

The ground conductor 160 may take several forms and is illustrated hereas a centrally located pin 160. In each configuration, the adhesivebinder 50 enables the VVM 100 to adhere directly to the metalconductors. The ground conductor 160 may act as either a circuit groundor a shield ground, as desired.

As illustrated, at least one quantity of VVM 100 protects one or moresignal conductors 156 from a transient voltage spike. The protectedconnector 150 in turn can protect other electrical devices that areeither electrically upstream or downstream from the connector 150.

Referring now to FIG. 12, the VVM 100 having the integrally adhesivebinder 50 is used with a ribbon cable connector 170. The VVM 100 can beused with any type of ribbon cable connector, such as a male, female,straight lead, right angle, straight lead/wire wrap and right angle/wirewrap version of a socket connector, D-connector, PCB connector, cardedge connector, dip connector, pin connector or termination jumper. TheVVM 100 may be implemented in a plug or receptacle type of ribbonconnector 170.

The ribbon connector 170 includes a body 172 that is constructed of anysuitable material and in an embodiment is plastic. The body 172, in bothplug and receptacle implementations, at least partially encompasses aplurality of conductors 176. The conductors 176 are substantiallyparallel with the walls of the body 172. If the body 172 is a plug, theconductors 176 are pins. If the body 172 is a receptacle, the conductors176 are sockets that receive pins. The ribbon connector 170 may secureany number of input/output signal conductors 176. One or more of theconductors 176 may be a ground conductor. Normally, a separate circuitground or shield ground 186 is provided. A ground strip 187 connects tothe ground pin 186 and provides the proper spacing so that a voltagetransient dissipates from one of the signal conductors 176 to the groundstrip 187 rather than to another signal conductor 176.

Between the body 172 and a second mating body 178 lies a ribbon cable180. Ribbon cable 180 may be any suitable cable including a gray flatcable, color coded flat cable, twisted pair flat cable and roundjacketed/shielded flat cable. In the illustrated embodiment, the secondbody 178 is a plug that fits over the receptacle body 172. Pins 182housed inside the plug body 178 pierce the insulation of the cable 180and create electrical contact with conductors inside the cable.

In the illustrated embodiment, at least one and possibly a plurality ofquantities of VVM 100 directly secure to the receptacle body 172 and theconductors 176 via the intrinsically adhesive property of the binder 50.The receptacle body 172 includes a substrate 184, which can be apolymer, a PCB material such as FR-4 or a polyimide. The VVM 100 can beapplied to either the top or bottom surfaces of the substrate 184. In analternative embodiment, traces are applied to the substrate 184 throughany suitable method. The traces electrically connect the signalconductors 176 to the VVM 100, the VVM 100 to the ground conductor 186,or both.

As illustrated, at least one quantity of VVM 100 protects one or moresignal conductors 176 of the ribbon cable connector 170 from a transientspike That is, the signal conductors 176 can shunt an overvoltage to theground pin 186. The ribbon connector 170 can in turn protect electricaldevices that are either electrically upstream or downstream from theconnector 170.

Referring now to FIG. 13, the VVM 100 having the integrally adhesivebinder 50 is used with a data or telecommunications connector 190. TheVVM 100 can be used with any type of data/telecom connector. In anembodiment, connector 190 is an eight conductor RJ-45 connector,commonly used in data networks, such as local area networks (“LAN's”),wide area networks (“WAN's”) and the like. In another embodiment,connector 190 is six conductor RJ-11 connector, commonly used inresidential and in certain commercial telephone systems.

The connector 190 includes a body 192, much of which has been cut awayin FIG. 13 to show the circuit protection provided by the VVM 100. Thebody 192 is constructed of any suitable material and in an embodiment isplastic. The body secures a number of signal conductors 194. The signalconductors 194 are bent appropriately to engage mating signal conductorsof a plug (not illustrated). The plug is inserted into the data/telecombody 192 in the direction of arrow 196. When the plug inserts into thebody 192, spring portions 198 of the signal conductors 194 bend so thata spring force is applied to the electrical connection between matingconductors.

In the illustrated embodiment, opposing ends 202 of the conductors 194electrically communicate directly with one or more quantities of VVM100, which is directly applied to substrate 204 via the intrinsicallyadhesive binder 50. VVM 100 directly electrically couples the signalconductors 194 to a ground conductor 206. As above, the ground conductor206 is properly positioned, spaced closer to each of the signalconductors 194 than the signal conductors 194 are to each other. Inanother embodiment, the ends 202 of the conductors 194 electricallyconnect with traces to which the VVM 100 adheres. In a furtherembodiment, the VVM 100 electrically connects to the ends 202 of thesignal conductors 194 via wire bonds.

Similarly, the VVM 100 in an embodiment, directly adheres to the groundconductor 206. In another embodiment, the ground conductor 206electrically communicates with the VVM 100 via one or more tracessecured to the substrate 204. In a further embodiment, the VVM 100electrically communicates with the ground conductor 206 via a bond wire.

In the above described manner, one or more or all of the signalconductors 194 may be protected from a transient voltage. Because LAN'sor WAN's typically encompass large distances between grounding points,ESD and EOS transients between the grounding points are seriousproblems. Devices such as air conditioners, heaters, elevators, copiersand laser printers, etc., can cause high levels of spikes and transientsin buildings having LAN's. The protected data/telecom connector 190protects devices connected to a network through the connector 190 fromtransient voltages occurring over the data lines of the network.Likewise, the connector 190 protects the data lines from an overvoltageevent emanating from a device connected to the network.

Referring now to FIGS. 14 and 15, other embodiments of the VVM 100applied to telecommunications connectors are illustrated. Theconfigurations illustrated in FIGS. 14 and 15 represent any type ofdata/telecom connector. In FIG. 14, only the relevant portion of theconnector 210 is illustrated. The connector 210 includes a plurality ofsignal conductors 212 with the bent ends 214, wherein the bent ends 214mate with conductors or a data/telecom plug (not illustrated) asdescribed above. The plug travels in the direction of the arrow 196,which inserts into the connector 210.

A body 216, cutaway for purposes of illustration, houses a shield 218,which is constructed of any suitable conductive material. The view ofFIG. 14 is generally from underneath the connector as it is illustratedin FIG. 13. The shield 218 therefore fits on top of and in back of theconductors 212.

The shield defines one or more cutout spring tabs 220. That is, the thinmetal shield 218 is stamped or cut along three sides of each tab 220,wherein the tab 220 is bent inward along the edge 222. The tabs 220 maybe bent inward to any desired angle less that 90°. When the shield 218is placed over the conductors 212, the tabs 220 contact the conductors212 and bend back towards 0°. The tabs 220 are therefore biased tomaintain electrical contact with the conductors 212.

A quantity of VVM 100, having the self-curing intrinsically adhesivebinder 50 is directly applied to the tabs 220, between the tabs 220 andthe conductors 212. The VVM 100 acts as an open circuit in its highimpedance state, so that little current normally flows from theconductors 212 to ground 218. When an ESD transient occurs, the VVM 100switches to its low impedance state, so that the transient spike shuntsto the shield ground 218.

In an embodiment, a stencil is used to apply a plurality of quantitiesof VVM 100 to a plurality of tabs 220. In another embodiment, a stencilis used to apply a plurality of quantities of VVM 100 to a single tab220 that spring-loads and causes contact to occur with a plurality ofconductors 212. In a further embodiment, a layer of the VVM 100 materialis first self-adhered to a large area of the shield 218, wherein aplurality of tabs 220 are then stamped so that each has an individualquantity of VVM 100. In yet another embodiment, a layer of the VVM 100is first self-adhered to a large area of the shield 218, wherein one ormore tabs 220 that each contact a plurality of conductors 212 isstamped.

Referring to FIG. 15, which is a side view of FIG. 14, a variation ofthe connector 210 of FIG. 14 is illustrated as a new connector 230. Asbefore, the body 216 is cutaway to reveal a portion of the shield 218.The shield 218 has been stamped so that the tab 220 bends inward alongthe edge 222 between the shield 218 and the conductor 212. The tabincludes a quantity of VVM 100 having the self-adhesive binder 50 of thepresent invention.

The signal conductor 212 has the bent spring portion 214 that is adaptedto mate with a conductor of a plug (not illustrated), wherein the pluginserts into the connector 230 in the direction indicated by the arrow196. In one embodiment, a coupling capacitor 232 is disposed between theVVM 100 on the tab 220 and the signal conductor 212. Tab 220, VVM 100,capacitor 232 and signal conductor 212 are connected in series in onepreferred embodiment. The capacitor 232 has a capacitance and voltagerating appropriate to handle a DC voltage of 2500 volts. That is, thecoupling capacitor 232 is designed to block out high levels of DCvoltage, such as those imposed during high potential [HI-POT] testing,to which LAN or Ethernet systems may become exposed.

The VVM 100 also adheres to and makes electrical contact with thecapacitor 232. The capacitor 232 may also be soldered or otherwiseelectrically connected to the conductor 212. The spring loading of thetab 220 also holds the capacitor 232 in place. The order of thecapacitor 232 and the VVM 100 may be reversed. It should also beappreciated that in FIGS. 14 and 15, the stamped tabs 200 may be usedalternatively with a VVM device (not illustrated) that uses any VVMknown to those of skill in the art.

FIGS. 11 through 15 illustrate that the VVM 100, through the binder 50,can be applied directly to a substrate, wherein the substrate is used ina piece of electrical equipment, such as a connector. Besides thevarious connectors illustrated, it should be appreciated that thesubstrate can be placed in other types of connectors, such as digitalvideo interfacing (“DVI”) connectors, analog to digital converter(“ADC”) connectors, etc., as well as other types of equipment, such asaudio headsets, camcorders, televisions, radios, personal email devices,computers, etc.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications may be madewithout departing from the spirit and scope of the present invention andwithout diminishing its attendant advantages.

1 A circuit carrier comprising: a first insulating layer; a secondinsulating layer; first and second electrodes positioned between thefirst and second insulating layers and separated from each other by agap; and a voltage variable material (“VVM”) that protects against anelectrostatic discharge (“ESD”) event, the VVM located in the gapbetween the first and second insulating layers and contacting the firstand second electrodes, wherein at least one insulating layer has aminimum thickness that is determined by and greater than or equal to (i)an ESD magnitude rating divided by (ii) a dielectric strength of the atleast one insulating layer.
 2. The circuit carrier of claim 1, whereinthe VVM is provided so that it is substantially flush with the first andsecond electrodes.
 3. The circuit carrier of claim 1, wherein at leastone of the first and second insulating layers is made of a materialselected from the group consisting of: FR-4, epoxy resin, ceramic, resincoated foil, teflon, polyimide and glass.
 4. The circuit carrier ofclaim 1, wherein the first electrode is a signal conductor and thesecond electrode is a ground/shield conductor.
 5. The circuit carrier ofclaim 1, which includes a plurality of first electrodes that are signalconductors, the second electrode being a ground/shield conductor, and aplurality of gaps between the first electrodes and the second electrode,and wherein the VVM is located in the gaps between the first and secondinsulation layers and contacts the first electrodes and the secondelectrode.
 6. The circuit carrier of claim 1, wherein the gap is a firstgap and which includes third and fourth electrodes positioned betweenthe first and second insulating layers and separated from each other bya second gap, and wherein the VVM is located in the second gap andcontacts the third and fourth electrodes.
 7. The circuit carrier ofclaim 6, wherein the first and third conductors are signal conductorsand the second and fourth conductors are ground/shield conductors. 8.The circuit carrier of claim 1, wherein the first and second conductorsare conductors of a high-definition multimedia (“HDMI”) interface, auniversal serial bus (“USB”) interface or a FireWire interface.
 9. Thecircuit carrier of claim 8, which is located in a connector housing ofthe the HDMI, USB or FireWire interface.
 10. The circuit carrier ofclaim 1, which includes at least one third electrode located on a sideof at least one of the first and second insulating layers that isopposite the VVM and the first and second electrodes.
 11. The circuitcarrier of claim 10, which includes (i) at least one fourth electrodecreating at least one gap with the third electrode located on saidopposite side and (ii) VVM located in the gap between the third andfourth electrodes, the VVM contacting the third and fourth electrodes.12. The circuit carrier of claim 11, which includes at least oneadditional insulating layer covering the third and fourth electrodes andthe VVM placed in the gap between the third and fourth electrodes. 13.The circuit carrier of claim 1, which is (i) small enough to be placedinside of a surface mountable component or (ii) large enough to hold aconnector that connects the board to a mating unit.
 14. The circuitcarrier of claim 1, wherein the VVM includes an insulating binder thathas at least one characteristic selected from the group consisting ofbeing: (i) self-adhering and (ii) self-curing.
 15. The circuit carrierof claim 1, wherein the VVM includes an insulating binder, (i)semiconductive particles with a doped core and a shell located about thecore held in the binder and (ii) conductive particles held in thebinder.
 16. The circuit carrier of claim 1, wherein the VVM includes aninsulating binder, (i) semiconductive particles held in the binder and(ii) conductive particles consisting essentially of a single materialheld in the binder.
 17. The circuit carrier of claim 1, wherein the VVMincludes an insulating binder, (i) first conductive particles thatinclude a conductive core and a shell located about the core held in thebinder and (ii) second conductive particles each comprising asubstantially pure material held in the binder.
 18. The circuit carrierof claim 1, wherein the VVM includes an insulating binder, (i) firstconductive particles held in the binder that include a conductive coreand a shell located about the conductive core, (ii) second conductiveparticles each comprising a substantially pure material held in thebinder and (iii) particles with a semiconductive core and a shelllocated about the semiconductive core held in the binder.
 19. Thecircuit carrier of claim 1, wherein the VVM is applied in the gap via aprocess selected from the group consisting of: (i) stencil printing withtrimming, (ii) stencil printing without trimming, (iii) screen printingwith trimming, (iv) screen printing without trimming, (v) controlleddispensing with trimming, (vi) controlled dispensing without trimming,(vii) pick and place dispensing with trimming and (viii) pick and placedispensing without trimming.
 20. A high-definition multimedia interface(“HDMI”) signal conductor comprising: a plurality of positive andnegative signal line pairs and a shield line located between eachpositive and negative signal line pair, wherein at least two of thesignal lines are located adjacent to one of the shield lines and anothersignal line; and voltage variable material (“VVM”) placed in electricalcommunication with the positive and negative signal line pairs and theshield lines so that (i) a first path from each positive or negativesignal line to its closest shield line is shorter than a (ii) secondpath from each positive or negative signal line to its closest adjacentpositive or negative signal line.
 21. The HDMI signal conductor of claim20, wherein the first and second paths lie in substantially a sameplane.
 22. The HDMI signal conductor of claim 20, wherein the first andsecond paths lie in substantially perpendicular planes.
 23. The HDMIsignal conductor of claim 20, wherein the VVM is located in a housing,the VVM placed via the housing in electrical communication with thepositive and negative signal line pairs and the shield lines.
 24. TheHDMI signal conductor of claim 23, wherein the housing includes internalcircuitry establishing the first and second paths, and wherein the VVMis placed in contact with the circuitry.
 25. The HDMI signal conductorof claim 23, wherein the housing is a housing of a connector located atan end of a cable carrying the signal lines and shield lines.
 26. TheHDMI signal conductor of claim 20, which includes a frame ground inaddition to the shield lines.
 27. A voltage variable material (“YVM”)comprising: an insulating binder; first conductive particles with a coreand a shell held in the insulating binder; and second conductiveparticles without a shell held in the insulating binder.
 28. The VVM ofclaim 27, wherein the insulating binder has a characteristic selectedfrom the group consisting of: (i) including a polymer resin, (ii) beingdissolved in a solvent and thickened with an agent, (iii) beingself-curable, (iv) including silicone and (v) any combination thereof.29. The VVM of claim 27, wherein at least one of the first and secondconductive particles has a bulk conductivity greater than 10 (ohm-cm)⁻¹.30. The VVM of claim 27, wherein at least one of the first and secondconductive particles is made of a material selected from the groupconsisting of: nickel, carbon black, aluminum, silver, gold, copper,graphite, tungsten, zinc, iron, stainless steel, tin, brass, zirconium,iopium, titanium and any combination thereof.
 31. The VVM of claim 27,wherein the shell of the first conductive particles includes an oxidelayer.
 32. The VVM of claim 27, wherein the second conductive particlesare agglomerated from smaller conductive particles.
 33. The VVM of claim32, wherein the smaller conductive particles have an average size on theorder of nanometers.
 34. The VVM of claim 32, wherein the secondconductive particles are (i) substantially spherical or (ii) at leastslightly elongated.
 35. The VVM of claim 27, wherein the firstconductive particles have an average size of about 0.1 to about fiftymicrons.
 36. The VVM of claim 27, wherein the second conductiveparticles have an average size of about 0.02 microns to about 5 microns.37. The VVM of claim 27, wherein the shell on the first conductiveparticles has an average thickness on the order of nanometers.
 38. TheVVM of claim 27, wherein the first conductive particles are provided ina concentration of about 35% to about 80% by volume.
 39. The VVM ofclaim 27, which includes at least one additional type of particleselected from the group consisting of: insulative particles,semiconductive particles and doped semiconductive particles.
 40. Avoltage variable material (“VVM”) comprising: an insulating binder;first conductive particles with a core and a shell held in theinsulating binder; second conductive particles without a shell held inthe insulating binder; and semiconductive particles with a core and ashell held in the insulating binder.
 41. The VVM of claim 40, whereinthe core of the semiconductive particles includes a material selectedfrom the group consisting of: silicon, silicon carbide, barium titanate,boron nitride, boron phosphide, cadmium phosphide, germanium, indiumphosphide, magnesium oxide, silicon, zinc oxide, zinc sulfide, and anycombination thereof.
 42. The VVM of claim 40, wherein the semiconductiveparticles have a conductivity of about 10 to 10⁻⁶ (ohm-cm)⁻¹.
 43. TheVVM of claim 40, wherein the semiconductive particles have an averagesize of about 0.3 to about 30 microns.
 44. The VVM of claim 40, whereinthe shell of the semiconductive particles has at least onecharacteristic selected from the group consisting of: being insulative,having an average thickness of about 100 to 10,000 Å, including silicondioxide, including epitaxial silicon and including glass.
 45. The VVM ofclaim 40, wherein the semiconductive particles are doped with a dopantmaterial.
 46. A voltage variable material (“VVM”) comprising: aninsulating binder; only first conductive particles with a core and ashell held in the insulating binder.
 47. The VVM of claim 46, whereinthe insulating binder has a characteristic selected from the groupconsisting of: (i) including a polymer resin, (ii) being dissolved in asolvent and thickened with an agent, (iii) being self-curable, (iv)including silicone and (v) any combination thereof.
 48. The VVM of claim46, wherein the core of the conductive particles is made of a materialselected from the group consisting of: copper, aluminum and aluminumnitride.
 49. The VVM of claim 46, wherein the shell includes silica oran oxide layer.
 50. The VVM of claim 46, wherein the conductiveparticles have an average size of about 2 to about twenty microns. 51.The VVM of claim 46, wherein the shell has an average thickness on theorder of nanometers.
 52. The VVM of claim 46, wherein the conductiveparticles are provided in a concentration of about 35% to about 75% byvolume.
 53. A method of manufacturing a circuit carrier comprising thesteps of: (a) providing a first electrode on a first insulating layer;(b) providing a second electrode on the first insulation layer andspacing the first and second electrodes apart to form a gap between theelectrodes; (c) screen printing/stenciling a layer of voltage variablematerial (“VVM”) into the gap so as to contact the first and secondelectrodes; and (d) providing a second insulating layer over at least aportion of the electrodes and the VVM so that the second insulatinglayer has a minimum thickness that is greater than or equal to (i) anelectrostatic discharge (“ESD”) magnitude rating of the VVM divided by(ii) a dielectric strength of the second insulating layer.
 54. Themethod of claim 53, which includes screen printing/stenciling the VVMinto the gap so that the VVM is flush with the first and secondelectrodes without trimming the VVM after the screen printing/stencilingstep.
 55. The method of claim 53, which includes the step of trimmingthe VVM so that the VVM is flush with the first and second electrodes.56. The method of claim 53, which includes repeating steps (a) to (d)where the second insulating layer becomes the first insulating layer ofrepeated steps (a) and (b) and a third insulating layer is applied inrepeated step (d).
 57. A method of manufacturing a circuit carriercomprising the steps of: (a) providing a first electrode on a firstinsulating layer; (b) providing a second electrode on the firstinsulation layer and spacing the first and second electrodes apart toform a gap between the electrodes; (c) using an apparatus that holds andstores voltage variable material (“VVM”) under pressure to dispense theVVM into the gap so as to contact the first and second electrodes; and(d) providing a second insulating layer over at least a portion of theelectrodes and the VVM so that the second insulating layer has a minimumthickness that is greater than or equal to (i) an electrostaticdischarge (“ESD”) magnitude rating of the VVM divided by (ii) adielectric strength of the second insulating layer.
 58. The method ofclaim 57, which includes using the apparatus to apply the VVM into thegap so that the VVM is flush with the first and second electrodeswithout trimming the VVM after the screen printing step.
 59. The methodof claim 57, which includes the step of trimming the VVM so that the VVMis flush with the first and second electrodes.
 60. The method of claim57, which includes repeating steps (a) to (d) where the secondinsulating layer becomes the first insulating layer of repeated steps(a) and (b) and a third insulating layer is applied in repeated step(d).
 61. The method of claim 57, wherein the apparatus mechanicallypressurizes the VVM, pneumatically pressurizes the VVM or atomizes theVVM.
 62. The method of claim 57, which includes moving the apparatus inat least one direction to dispense the VVM to a desired location on thefirst insulating layer.
 63. The method of claim 57, which includesmoving the apparatus in at least one direction to dispense the VVMcontinuously to form a trace of VVM on the first insulating layer.